The surface chemistry of oxygen and oxygenates on Rutile TiO2(110) is of great interest for various applications such as heterogeneous catalysis and photo catalysis. Though it is generally accepted that surface defects are active sites, the role of subsurface defects is under debate. We have therefore investigated the influence of the bulk defect density on the reductive coupling of benzaldehyde to stilbene as a model system. Using IRRAS we identify stilbene diolate as a reduction intermediate. The concentration of this intermediate is proportional to the bulk defect density, whereas adsorption of benzaldehyde at lower temperatures is not affected, which indicates a dominant role of Ti interstitials at temperatures above 400 K.

The interaction of molecules with low coordinated sites and possible modification of surfaces caused by adsorbates are of crucial importance for an understanding of chemical processes on surfaces. Herein, CO adsorption on a stepped Au(332) surface is investigated by combining infrared spectroscopy and density functional theory calculations. It is shown that infrared spectroscopic characterization of isotopically diluted mixtures allows distinguishing different components. These components exhibit significantly different adsorption energies as well as vibrational characteristics which can be understood with the help of a theoretical analysis based on density functional theory (DFT). In addition, it is shown that CO induces a restructuring of the surface, leading to a significantly more heterogeneous ensemble of adsorption sites and a significant reduction of sites with the highest CO adsorption energy.

Electron-assisted hydroxylation of single-crystalline silica bilayer films grown on Ru(0001) is studied by high-resolution electron energy loss spectroscopy (HREELS) and electron paramagnetic resonance (EPR) spectroscopy. The HREELS results reveal the formation of several hydroxyl species whose number and speciation depend on the defect structure of the film. For incomplete bilayer films, which exhibit nanometer-sized holes in the bilayer, the level of hydroxylation is significantly larger than for complete films. HREEL spectra taken in off-specular geometry provide evidence for the presence of hydroxyl groups with a transition dipole moment almost parallel to the surface for complete and incomplete bilayer films. Hydroxylation with isotopically labeled water (H2 18O) reveals a clear difference between the two casesOH species on the incomplete film almost exclusively contain oxygen from water, while the more ideal film exhibits OH groups with oxygen atoms stemming from both water and the silica film. These observations not only indicate that the degree of hydroxylation is significantly enhanced for the incomplete film but also that the reaction mechanism for hydroxylation at defect sites of this film is different. To gain insight into the reaction mechanism of electron-assisted hydroxylation, in situ EPR spectroscopy of electron-bombarded adsorbed ice layers was combined with infrared (IR) spectroscopy and mass spectrometry. We show that the electron bombardment removes a significant part of the water layer and produces different reactive paramagnetic species, namely, O2D, D, and solvated electrons, which may be trapped at low temperatures. The interaction of the silica film with such species may lead to splitting Si–O bonds even for covalently saturated silica structures as found in the ideal bilayer film and thus provide insight into possible reaction mechanisms.

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